[volt-nuts] Reference in Signametrics 7.5 digit DMM?

[Jan Fredriksson]

Hi,

Does someone know what reference is used in the Signametrics/Agilent 2060x?

I have had an unused SMU2064 on the shelf for some time. Recently I
powered it up and found it very noisy compared to my LTZ1000 based
DMMs. It seems I can get around 6.5 digit resolution from this DMM,
noise is in the order of 10uV on the 10V range.

One idea is that the reference is the noise source. So I ripped the
box open, only to find that a number of ICs are defaced (sandpaper /
anonymous) and none that I can identify as a reference.

I'd like to try replace the reference with something better, see if it
helps get the noise level down, before attempting calibrating it. The
meter otherwise mostly contains components from Analog Dev.

Much of the circuitry is sandwiched between two boards so it's hard to
test under power. (No worries, it runs on 5V from USB only).

So does anyone know what reference is used, or better, has any
documentation / schematics?

Jan